Transmyocardial Revascularization
In the treatment of heart disease, one method of improving myocardial blood supply is called transmyocardial revascularization (TMR), the creation of channels in the myocardium of the heart. The procedure using needles in a form of surgical "myocardial acupuncture" has been used clinically since the 1960s. Deckelbaum. L. I., Cardiovascular Applications of Laser Technology, Lasers in Surgery and Medicine 15:315-341 (1994). The technique relieves ischemia by causing angiogenesis and allowing blood to pass from the ventricle through the channels either directly into other vessels communicating with the channels or into myocardial sinusoids which connect to the myocardial microcirculation.
In the reptilian heart, perfusion of the myocardium occurs via communicating channels between the left ventricle and the coronary arteries. Frazier, O. H., Myocardial Revascularization with Laser--Preliminary Findings, Circulation, 1995; 92 [suppl II]:II-58-II65. There is evidence of these communicating channels in the developing human embryo. In the human heart, myocardial microanatomy involves the presence of myocardial sinusoids. These sinusoidal communications vary in size and structure, but represent a network of direct arterial-luminal, arterial-arterial, arterial-venous, and venous-luminal connections. This vascular mesh forms an important source of myocardial blood supply in reptiles but its role in humans is poorly understood.
This is confirmed by recent research and a recent article. A greater proportion of reptilian endocardium and myocardium is supplied with oxygenated blood from the left ventricle itself, as opposed to the coronary arteries. Reptilian endocardium is relatively thicker and more sponge-like than human myocardium, deriving from the extensive network of sinusoids and large channels emanating from the left ventricle and richly innervating the myocardium, thereby providing an increased effective surface area for blood flow, also known as "washing", and transfer of oxygen and nutrients to the myocardium. In the research protocol, after explanation and instrumentation, alligator hearts were perfused via the coronary arteries as well as via "washing" from the left ventricle. Using microspheres to estimate myocardial perfusion in the beating hearts, it was shown that although the epicardium was well perfused by the coronary arteries, a significant proportion of endocardial perfusion was from the ventricular chamber rather than the coronary arteries. Kohmoto, T. et al, Assessment of Transmyocardial Perfusion in Alligator Hearts, Circulation, Vol. 95, No. 6, Mar. 18, 1997.
Apparatus and methods for extending the thickness of endocardial tissue, and increasing oxygen and nutrient transport by washing of blood through the left ventricle, are virtually unknown. Conventionally, a process called transmyocardial revascularization is directed to forming a discrete number of spaced-apart channels, surgically from an epicardial surface through epicardium (TMR) or percutaneously through the left ventricle directly into myocardial tissue (PTMR). However, conventional TMR/PTMR does not create a dense pattern of stimulus injuries placed to simulate extension of the porous endocardium. TMR also does not focus treatment on the endocardial/myocardial boundary regions where ventricular washing flow via endocardium can enhance angiogenesis. Furthermore, treating hidden zones of hibernating, infarct-damaged or other types of tissue with a denser pattern of stimulation pathways is desirable and may be accomplished using the apparatus and methods for selective treatment of the endocardial/myocardial boundary.